In the combustion of a fuel, such as coal, oil, natural gas, peat, waste, etc., in a combustion plant, such as a power plant or a waste incineration plant, a process gas is generated. For separating nitrogen oxides, usually denoted NOx, from such a process gas, often referred to as a flue gas, a method is frequently used, in which a reducing agent, usually ammonia or urea, is mixed with the flue gas. The flue gas, mixed with said ammonia or urea, is then passed through a catalyst in which the reducing agent reacts selectively with the NOx to form nitrogen gas and water vapour. Usually the catalyst is installed in a so called Selective Catalytic Reduction reactor (SCR reactor).
In many processes, the concentration of NOx of the flue gas is not evenly distributed over the cross-section of the SCR reactor. This poses a problem, since a stoichiometric ratio between the NOx and the reducing agent is essential for achieving a good reduction of the NOx content of the flue gas and a low slip of the reducing agent from the SCR reactor.
Also, the temperature and/or velocity of the process gas may vary over the cross-section of a gas duct forwarding process gas of a power plant.
U.S. Pat. No. 8,066,424 discloses a mixing device which is arranged in a flow channel for mixing a fluid flowing through the channel. The mixing device has a plurality of mixer disks arranged in mixer disk rows having row axes running across the main direction of flow. The fluid flowing through the system is mixed by leading edge vortices generated by the mixer disks.
Although mixing of process gas is achieved to some extent by the arrangement disclosed in U.S. Pat. No. 8,066,424, a more efficient mixing of process gas of a power plant is desired.